This type of method is known from EP 0 510 457 B1, which is incorporated herein by reference.
Methods of this type are preferably used in motor vehicles equipped with equalizing gears and/or power dividers. To avoid spinning of individual drive wheels of the vehicle on smooth road surfaces, the above-mentioned gears, which are for the most part designed as differential gears, are equipped with a locking device, through which the parts which are uncoupled from each other by the gear in normal operation can be rigidly connected to each other.
Such locking devices may be actuated manually by the driver when necessary, or to increase riding comfort and safety, may be actuated automatically by a control signal emitted by a control device, when certain external conditions exist, as detected by sensors.
In the prior art, a locking device for an equalizing gear or a power divider is actuated automatically in the above-described manner, when the difference between the speeds of the rotating parts attached to the output shafts of the gear exceed a predetermined limit value. In order to avoid damage to the locking device or to the gear, this limit value is kept relatively low, i.e., the locking device is actuated at a low difference between the speeds. In the case of a very large difference in speeds, actuation would not be permissible, because damage to the locking device or to the gear would be likely to occur. Therefore, when differences in speeds increase very rapidly, the locking device is not actuated until the difference in speeds is reduced. During this period of time, however, a dangerous driving condition may occur, because of the spinning of individual drive wheels. Depending on external circumstances, this dangerous driving condition may last for an indeterminate, long period of time.
It is therefore an object of the present invention to provide a method and apparatus for the synchronization of two rotating parts, which can be achieved in as short a time as possible, regardless of the speed behavior of the rotating parts, and without incurring any damage to the parts of the motor vehicle.
In the following description, the "synchronization of rotating parts" is to be understood as the adaptation or approach of the speeds of the rotating parts to each other.
The present invention achieves synchronization of the rotating parts in a relatively short period of time, without the occurrence of sudden impacts or jolts, even when the differences between the speeds are very large, or are increasing very rapidly. As a result, damage to gears, the locking device, the rotating parts, or other parts of the motor vehicle are avoided.
Through the use of a braking device, in addition to a locking device, it is possible to adapt the speeds of rotating parts to each other gradually, rather than suddenly. Therefore, spinning of the slower rotating wheel, or wheels, which may occur as a result of sudden synchronization via a locking device, can also be avoided, providing a particularly safe behavior of the vehicle.
In an advantageous further development of the invention, an adaptation value is determined from the speeds in order to ascertain the adaptation or approach tendency of the speeds to each other. When this adaptation value has reached a predetermined limit value, the rotating parts are synchronized through actuation of a locking device. By this, determination of the right moment for actuation of the locking device can be done in a very simple manner. Preferably, a microprocessor is used to determine the adaptation value, and to compare it with the limit value.
The method for determining this adaptation value may consist of a number of different procedures and calculations, so that the method according to the invention may have multiple applications. It is possible, for example, to take into account differences between the speed values from certain prior time periods, and to calculate a time function from these differential values by means of interpolation. Thus, a point in time for the matching of the speeds can then be predicted by extrapolation. In this case, the adaptation value would be a differential value of the speeds, calculated from the time function in such manner that, when the predetermined limit value is reached, it causes a locking of the gear precisely at that time, taking into account a gear-specific time delay (idle time) when the speeds become equal.
In an advantageous further development of the invention, the adaptation value has at least a component which depends on the difference between the speeds. Thus, a very simple calculation is possible.
In another advantageous further development of the invention, the adaptation value has at least one component which depends on the derivative of the difference between the speeds. Moreover, a combination of these last two mentioned further developments of the invention is also advantageous. One advantage of this combination is that a prediction on the expected coinciding of the speeds can be made, so that possible idle times which may occur in actuating the locking device can be taken into account. As a result, it is not necessary to store a great number of values from a past time period.
It is possible to apply the invention in combination with an equalizing gear, which is located between the wheels of a vehicle axle, as well as with a power divider, which is located between two vehicle axles, e.g., in a vehicle with all-wheel drive. The same type of gear, preferably a differential gear, is often used for both the equalizing gear and the power divider. The locking device is then called a differential lock. In addition, other types of locking devices are also possible.
In another advantageous further development of the invention, the braking device causes a braking of its individually assigned rotating part, whereby the braking force can be adjusted. This makes it possible to obtain an especially fine-tuned, stepped adaptation of the speeds to each other, even when the difference between the speeds is very large. It is especially advantageous when braking systems assigned to the synchronized wheels of a motor vehicle can be used directly. Since such braking systems are generally already present in motor vehicles, the present invention can be used at little additional cost and in many different ways; in particular, in motor vehicles with a system for drive slip regulation (ASR).
In another advantageous further development of the invention, the braking device and/or the locking device is actuated only when an auxiliary value exceeds an assigned auxiliary limit value. When applying the invention to a vehicle, the auxiliary value represents a measure of the drive slip of a wheel. In order to determine the auxiliary value, a vehicle velocity sensor signal, or the speed signals of wheels of a non-driven axle, preferably the steerable axle of the vehicle, can be used. By taking the auxiliary value into account, it is possible during turns, especially in tight turns, to prevent unwanted actuation of the braking devices and/or the locking device.